The most common use of sheet feed cassettes is in the printing, recording and copying fields. The sheet feed cassette houses a plurality of recording sheets having a predetermined size, with the sheets being set in a predetermined position within the cassette. The cassette is adapted for insertion into a copying, recording or printing apparatus. Such apparatus employ a system in which the recording sheets are fed seriatim from the cassette. This, however, requires the availability of different cassettes for each recording sheet size. Examples of this are disclosed in U.S. Pat. Nos. 4,277,165; 4,440,487 and 4,696,563.
Multiple cassettes housings of the three or more housing variety are provided in a number of copying, recording or printing apparatus, as disclosed in U.S. Pat. Nos. 4,804,997 and 4,862,220, to accommodate cassettes containing recording sheets of different sizes. In such an apparatus each cassette housing has associated with it preset operating parameters to accommodate the particular size of recording sheet for that housing. As an example, when recording on a large size recording sheet, such as A3, a greater optical scanning distance is required of the copying apparatus. Therefore, the housing that accommodates a cassette containing A3 recording sheets has a preset scanning distance to accommodate copying on A3 size sheets. This allows for precise scanning of the documents to be copied and results in a very efficient use of the apparatus' optical scanning system. It also increases the number of reproductions per unit time since the apparatus, on sensing the size of the sheet to be recorded upon, can adjust its scan so it matches precisely the travel distance for the size sheet to be recorded upon. With the scan matching precisely the size of the recording sheet, underscan of the image to be copied is avoided, since the scan will be identical to the size recording sheet to be recorded upon. Overscan is also avoided, since the scan will never be greater than the size of the sheet to be recorded upon. Recording efficiency is thereby improved. In addition, when scanning is based upon recording sheet size, it is possible to have auto-magnification, auto-paper select, edge erase and interframe erase, but these patents do not disclose a total solution, since they require multiple cassettes and the need for a copying apparatus having multiple housing slots.
To avoid the need for multiple size cassettes, a cassette capable of housing recording sheets of different sizes was developed and put into practical use. Such a cassette is called a universal cassette and consists of a cassette body capable of housing recording sheets up to a specified maximum size. The cassette has a movable rear guide adapted to adjust to the location of the rear edge (the edge that is furthest away from the edge initially inserted into the copying, printing or recording apparatus) and one or two movable side guides adapted to adjust to the location of the side edges of the recording sheet. The front edge, and perhaps one side edge, are maintained in position by fixed walls of the cassette.
While a universal cassette avoids the need to have multiple size cassettes, it doesn't resolve the problem of less than ideal operational parameters when commercially nonstandard sheet sizes are used. An illustration of this is a universal cassette used in a conventional copying, recording or printing apparatus, such as one having only one cassette housing. The optical scanning maybe adjusted, as shown in U.S. Pat. Nos. 4,579,333 and 4,780,740. However, these patents only address adjusting operational parameters when commercially standard size sheets are contained in the cassette. They do not have the ability to recognize other than commercially standard size sheets. This is inefficient, since the optical scanning travel distance is only set for commercially standard size sheets, irrespective of the size recording sheets used. Under these circumstances, the reproduction rates for certain sheet sizes, notwithstanding the actual size of the recording sheet, measured on a per unit time basis would be equal. In other words, when recording with sheets of commercially nonstandard size, a larger than necessary scanning distance is required. If a smaller scan distance were used, there would be unused space on the recording sheet. This results in a decrease in reproduction efficiency or inefficient use of the recording sheet, since there is either overscan or space on the recording sheet that is not utilized, even when using a universal cassette.